[dm-devel] Fwd: MD/DM and barriers (was Re: [patch] ext2/3: document conditions when reliable operation is possible)
Ric Wheeler
rwheeler at redhat.com
Thu Aug 27 17:13:18 UTC 2009
fyi - end of a very long thread, but I thought that dm had this fixed...
ric
-------- Original Message --------
Subject: MD/DM and barriers (was Re: [patch] ext2/3: document
conditions when reliable operation is possible)
Date: Thu, 27 Aug 2009 12:54:05 -0400
From: Jeff Garzik <jeff at garzik.org>
To: Ric Wheeler <rwheeler at redhat.com>
CC: Theodore Tso <tytso at mit.edu>, Rob Landley <rob at landley.net>, Pavel
Machek <pavel at ucw.cz>, Florian Weimer <fweimer at bfk.de>, Goswin von
Brederlow <goswin-v-b at web.de>, kernel list
<linux-kernel at vger.kernel.org>, Andrew Morton <akpm at osdl.org>,
mtk.manpages at gmail.com, rdunlap at xenotime.net, linux-doc at vger.kernel.org,
linux-ext4 at vger.kernel.org, corbet at lwn.net
On 08/27/2009 09:10 AM, Ric Wheeler wrote:
> One thing that does need fixing for some MD configurations is to stress
> again that we need to make sure that barrier operations are properly
> supported or users will need to disable the write cache on devices with
> volatile write caches.
Agreed; chime in on Christoph's linux-vfs thread if people have input.
I quickly glanced at MD and DM. Currently, upstream, we see a lot of
if (unlikely(bio_barrier(bio))) {
bio_endio(bio, -EOPNOTSUPP);
return 0;
}
in DM and MD make_request functions.
Only md/raid1 supports barriers at present, it seems. None of the other
MD drivers support barriers.
DM has some barrier code... but the above code was pasted from DM's
make_request function, so I am guessing that DM's barrier stuff is
incomplete and disabled at present.
I've been mentioning this issue for years... glad some people finally
noticed :)
Jeff
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo at vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
More information about the dm-devel
mailing list